Apparatus for propellant flow control at low mass flow rates in zero G environment

Abstract

An apparatus for use in space environments to control the flow of a propellant to a thruster at a low mass flow rate comprises an insulated body having a cavity therein defining a vaporizing chamber, a porous medium having a low liquid permeability disposed in the chamber, a conduit means for feeding a propellant liquid into the chamber and exhausting a propellant vapor from the vaporizing chamber, and a heating means communicating with the medium within the chamber for controllable heating of the liquid propellant in the chamber creating a variable liquid/vapor transition zone within the medium. The transition zone is responsive to the heating means to control the mass flow rate of propellant through the vaporizing chamber. As the liquid/vapor transition zone is moved upstream by increasing the heater output, and thus increasing the volume of vapor within the porous medium, mass flow through the porous medium is decreased. Conversely, movement of the liquid/vapor transition zone downstream through the medium by decreasing the heater output, and thus exposing more of the porous medium volume to liquid, increases the mass flow rate.

What is claimed is: 
     
       1. A fluid propellant vaporizing apparatus adapted for use in a zero gravity environment to control the flow of a propellant fluid therethrough comprising: a solid body having a cavity therein defining a vaporizing chamber;   a porous medium disposed in said chamber so as to separate said chamber into an inlet portion and an outlet portion, said medium having a low permeability to liquid propellant effective to limit the flow of said propellant fluid therethrough and between said chamber portions to less than 2 lbm/hr;   conduit means for feeding a propellant fluid into said inlet portion of said chamber and exhausting said propellant fluid from said outlet portion of said chamber; and   heating means communicating with said medium for controllably heating said propellant fluid in said chamber creating a variable liquid/vapor transition zone within said medium, said transition zone being responsive to said heating means to control the mass flow rate of propellant fluid through said vaporizing chamber.   
     
     
       2. The apparatus according to claim 1 wherein said body is a cylindrical canister having an outer wall and at least two concentrically spaced inner walls defining said vaporizing chamber between said inner walls, said inner walls containing said porous medium and having apertures therethrough for passage of said propellant into and out of said chamber. 
     
     
       3. The apparatus according to claim 1 wherein said medium is a self supporting annular cylindrical body. 
     
     
       4. The apparatus according to claim 1 wherein said medium is a plurality of capillary tubes arranged to direct said fluid from said inlet portion to said outlet portion. 
     
     
       5. The apparatus according to claim 3 wherein said medium is a ceramic material. 
     
     
       6. The apparatus according to claim 1 wherein said body is a cylindrical canister having an outer wall and a concentrically spaced inner wall defining a passage therebetween, said inner wall separating said chamber from said passage, said inner wall having a plurality of apertures therethrough for passage of said propellant fluid through said passage and said apertures into said inlet portion of said chamber. 
     
     
       7. The apparatus according to claim 6 wherein said porous medium is a tubular solid having an outer surface against said inner wall and an inside surface spaced inwardly of said outer surface, said medium having a low liquid permeability effective to limit passage of liquid propellant therethrough to a given maximum mass flow rate when said transition zone is near said inside surface. 
     
     
       8. The apparatus according to claim 3 wherein said porous medium has an outer surface and an inside surface spaced inwardly of said outer surface, said medium having a permeability effective to limit passage of liquid propellant therethrough to a maximum mass flow rate when said transition zone is near said inside surface and a minimum flow rate when said transition zone is at said outer surface. 
     
     
       9. The apparatus according to claim 8 wherein said heating means comprises a resistance heating element centrally disposed within said outlet portion of said chamber and spaced inwardly of said inside surface so as to form a vapor passage therebetween, said passage communicating with said conduit means for exhausting a vapor from said chamber. 
     
     
       10. The apparatus according to claim 9 wherein said apparatus is a cylindrical canister symmetrical about a central axis therethrough and said medium and said heater are coaxially spaced within said canister. 
     
     
       11. The apparatus according to claim 10 wherein said medium is a bed of capillary tubes axially aligned about said axis to direct said fluid from said inlet portion to said outlet portion. 
     
     
       12. The apparatus according to claim 8 wherein said heating means comprises at least two heaters embedded within said medium. 
     
     
       13. The apparatus according to claim 12 wherein said heaters are selectively controllable so as to vary the location of said transition zone in said medium. 
     
     
       14. The apparatus according to claim 13 wherein said apparatus is a cylindrical canister symmetrical about a central axis therethrough and said medium is coaxially spaced within said canister. 
     
     
       15. The apparatus according to claim 14 wherein said medium is a bed of capillary tubes axially aligned about said axis to direct said fluid from said inlet portion to said outlet portion. 
     
     
       16. The apparatus according to claim 12 wherein said body is a cylindrical canister having an outer wall and a concentrically spaced inner wall defining a passage therebetween, said inner wall separating said chamber from said passage, said inner wall having at least one aperture therethrough for passage of said propellant fluid through said passage and said aperture into said inlet portion of said chamber. 
     
     
       17. The apparatus according to claim 1 wherein said liquid permeability of said medium is uniform. 
     
     
       18. The apparatus according to claim 1 wherein said permeability of said medium varies radially. 
     
     
       19. The apparatus according to claim 18 wherein said permeability varies directly with the radial position within said medium. 
     
     
       20. The apparatus according to claim 18 wherein said medium comprises a plurality of concentric sleeves each having a different permeability. 
     
     
       21. The apparatus according to claim 20 wherein said medium is made of a ceramic material.